batman-adv: Kconfig, Add missing DEBUG_FS dependency

BATMAN_ADV_DEBUG is using debugfs files for the debugging log. So it
depends on DEBUG_FS which is missing as dependency in the Kconfig file.
Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>

net/batman-adv/Kconfig

@@ -62,6 +62,7 @@ config BATMAN_ADV_MCAST
 config BATMAN_ADV_DEBUG
 	bool "B.A.T.M.A.N. debugging"
 	depends on BATMAN_ADV
+	depends on DEBUG_FS
 	help
 	  This is an option for use by developers; most people should
 	  say N here. This enables compilation of support for